Microwave power receiving antenna



vit- 0 0 c. c. DAILEY MICROWAVE POWER RECEIVING ANTENNA 3 Sheets-Sheet 1 INVE N TOR Filed May 1, 1969 g 22: TTORNE YS CARROLL c DAILEY BY 27 Q 5 Sheets-Sheet 2 POWER SUPPLY 26 28) 3* 36 MICRO WAVE R LOAD GENER CONDI IONER FE G. 5

INVENTOR CARROLL C. DAILEY ORNEYS Oct. 20, 1970 c. c. DAILEY ,5

MICROWAVE POWER RECEIVING ANTENNA Filed May 1, 1969 3 Sheets-Sheet 5 FIG 7 INVEN TOR CARR OLL C. DAILEY A ORNE Y3 3,535,543 MICROWAVE POWER RECEIVING ANTENNA Carroll C. Dailey, Huntsville, Ala., assignor to the United States of America as represented by the Administrator of the National Aeronautics and Space Administration Filed May 1, 1969, Ser. No. 820,965 Int. Cl. H02j 1/00 U.S. Cl. 307-149 6 Claims ABSTRACT OF THE DISCLOSURE A microwave power receiving antenna array having a solid-state rectifier circuit at the center of each of a plurality of dipole antennas for conversion of the high-frequency energy to direct current. The device effectively and efficiently solves the problem of heat dissipation from the diode rectifier enclosure by construction of the dipole supporting posts, the antenna reflecter and the dipole elements as heat pipe devices. Each supporting post and the antenna reflector may either communicate for greater efficiency in dissipating heat or be physically separated to simplify fabrication.

ORIGIN OF THE INVENTION The invention described herein was made by an employee of the United States Government and may be manufactured or used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to power receiving antennas and more particularly to a rectifying dipole antenna array having a highly efficient structure for dissipation of heat from the rectifying circuit.

Description of the prior art One of the comparatively recent modes of electrical power transmission is power transfer by microwaves using frequencies as high as about 30 gigahertz. One attractive use of this type of power transmission is for powering helicopters or other types of aircraft from a remote location. Another use which appears attractive is transmission of power from a central manner space station, which can service a number of small independent subsatellites or experiment modules located distances as much as several kilometers away. Batteries in a subsatellite can be recharged with energy generated in the main space station, thus precluding the need for solar arrays or extra batteries on the subsatellite, increasing its versatility, and prolonging its useful life.

In the power receiving antenna for a microwave power transmission system, a rectifying circuit may be used to convert the high frequency energy to direct current. The diodes which transform the high frequency energy to DC are usually quite efiicient (approximately 70 to 90 percent). However, there is some loss of energy which ap pears as heat. This heat raises the temperature of the diodes. Also, the diodes and the antenna or antenna array are subject to the heating of the suns rays. These heating effects have the inherent disadvantage of limiting the amount of electrical power that can be handled by the array because of the temperature limits of the diodes. For

diodes of interest in space applications, this limit typically occurs at about 120 centigrade, although specific applications may show limits somewhat higher or lower.

In order to keep the diode temperature down, it is necessary to radiate heat to space. The area of the radiating surface available and the coatings applied to the sur- Patented Oct. 20, 1970 face determine how much heat can be radiated at a specific temperature. In the case of antenna dipoles the radiating area is small, since the conductors are narrow and the dipoles are also very small.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved microwave receiving antenna.

Still another object of this invention is to provide a microwave receiving antenna having the capability of efficient dissipation of heat from its rectifier circuits.

Yet another object of this invention is to provide a more efiicient microwave receiving antenna by modifying conventional elements of antenna structure so as to better radiate the heat from the antennas rectifier circuit.

These and other objects are accomplished in the present invention which provides at least one pair of dipole antenna elements supported by an enclosure containing a rectifying circuit comprising a plurality of diodes. Each enclosure and its corresponding pair of dipoles is mounted on a heat conducting support post, which in turn is mounted on a large antenna reflector.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood by the following detailed description when taken together with the accompanying drawings in which:

FIG. 1 is an isometric view of an orbiting space laboratory transmitting electrical power to a subsatellite.

FIG. 2 is a block diagram of a microwave power system capable of utilizing the present invention.

FIG. 3 is a plan view of a dipole having a bridge recti fier at its center, illustrating part of one embodiment of the present invention.

FIG. 4 is a side view of part of a microwave receiving antenna, which illustrates one embodiment of the present invention.

FIG. 5 is a horizontal sectional view of the support post taken along line 55 of FIG. 4 and showing the inner construction of the heat pipe support post.

FIG. 6 is a side view of the microwave power receiving antenna array showing one row of dipoles.

FIG. 7 is a plan view of one embodiment of the microwave power receiving antenna array, showing two rows of three dipoles mounted on a reflector.

DESCRIPTION OF THE PREFERRED EMBODIMENT With continued reference to the accompanying figures wherein like numerals designate similar parts throughout the various views and with initial attention directed to FIG. 1 there is illustrated an orbital space laboratory, designated generally by numeral 10, transmitting electrical power by microwaves to a subsatellite, designated generally by numeral 12. Laboratory 10 includes a spent rocket stage 14 having solar panels 16, docking adapter 18 and command modules 20 and 22. Solar panels 16 may be replaced by a nuclear power source in other versions of laboratory 10.

Referring now to FIG. 2, a microwave power system which includes the present invention is shown in block diagram form. Electrical power in the form of microwaves is furnished by microwave power generator 28 having power supply 30. Power transmitting antenna 24 is aimed at power receiving antenna 26 and transmits electrical power in the form of microwave beam 32 to receiving antenna 26. Subsatellite 12 uses this power received from beam 32 to charge its batteries or fuel cells or for powering electric thrusters. The energy in beam 32 is converted from high-frequency energy (approximately 2 megahertz to 30 gigahertz) to a direct current which is fed into power 3 conditioning equipment 34 to transform it to the actual voltages required for the load 36.

FIG. 3 shows a self-supporting, single, half-wave, Hertz antenna, designated generally by numeral 38, having a pair of dipole antenna elements 40. The conversion from high-frequency energy to direct current is accomplished by a plurality of diodes 42 which are connected in a bridge rectifier circuit 44 (shown in diagrammatic form). Rectifier circuit 44 is contained in dipole center enclosure 46 and is connected between the dipole elements 40 and a pair of output terminals 48. Dipole elements 40 are securely fastened to opposite sides of enclosure 46.

FIG. 4 ShOWs a single, half-wave dipole antenna 38 mounted on enclosure 46. Enclosure 46 is shown in vertical section so that diodes 42 may be seen, contained in potting compound 49. Enclosure 46 is mounted on support post 50 which is in turn mounted on an antenna reflector 52. Support post 50 is a hollow pipe which is closed at its upper end where it is fastened to enclosure 46 and open at its lower end where it is fastened to antenna reflector 52. Reflector 52 comprises a pair of metal walls 54 and 55, a pair of ends 56, and a pair of sides 57 (see FIG. 7) all of which make reflector 52 a closed container. However, the cavity of reflector 52 communicates with the lower end of support post 50, as described above.

Both support post 50 and antenna reflector 52 utilize known principles of operation of a heat pipe. As may be seen in both FIG. 4 and the horizontal sectional view of the support post shown in FIG. 5, all the interior surfaces of both support post 50* and reflector 52 are covered with a wicking material 58, which may be screen wire or a similar material. The communicating space enclosed by poth the support post 50 and the antenna reflector 52 together contains a heat transfer fluid 60, which may be water, lithium or a number of other substances which are easily vaporized.

FIGS. 6 and 7 are side and plan views, respectively, of a microwave power receiving antenna 26 having a plurality of half-wave dipole antennas 38. Each dipole 38 is supported by a corresponding dipole center enclosure 46 and support post 50. All dipoles 38 are mounted on one antenna reflector 52, so as to provide a combined broadside and collinear antenna array. Each support post 50 communicates with the antenna reflector 52 in a manner already described for FIG. 4 above. The internal construction of each support post 50 and the antenna reflector 52, including wicking material 58 and the presence of heat transfer fluid 60, is also as described for FIG. 4.

One cycle of operation of the microwave power receiving antenna 26 follows: Microwave power beam 32 is received on the dipole elements 40 of half-wave antenna 38. Bridge rectifier circuit 44 comprising diodes 42 rectifies the incoming high-frequency energy to convert it to direct current. Power conditioner 34 changes the form of the direct current as desired and transmits it to the load 36. Heat developed within enclosure 46 is absorbed by the top end of support post 50. Heat transfer fluid 60 absorbs heat from the end of support post 50- and is Vaporized. The vapor 62 then moves under vapor pressure down the support post 50 and passes into the inner portion of antenna reflector 52. When the vapor 60 reaches a comparatively cool spot on the surface of antenna reflector 52 (which would theoretically be midway between the hot spots caused by the heat input from the support post 50 or as far as possible from a support post 50), the vapor 62 condenses back to fluid 60 and forms deposits on the inner sides of antenna reflector walls 54 and 55, antenna reflector ends 56, and antenna reflector sides 57. The fluid 60 (condensate) then moves by means of capillary flow through the wicking material 58 back to the top of support post 50, where it absorbs more heat and starts the cycle over. In condensing, vapor 62 gives up heat which is absorbed by walls 54 and 55, ends 56, and sides 57. Thus, heat is distributed evenly to all parts of the surface of antenna reflector 52 so that reflector 52 is able to effectively dissipate this heat by radiation into space.

In an alternative arrangement of the invention the interior cavity of each support post 50 does not communicate with the interior cavity of the antenna reflector 52. Instead, the upper sidewall 54 has no openings. In this embodiment, each support post 50 as well as the antenna reflector 52 contains its own supply of heat transfer fluid 60, which cycles within the cavity available. Thus, heat is transferred down the support post 50 and passes by conduction through wall 54 of the antenna reflector 52. The heat is then transferred evenly to the walls of the antenna reflector 52 where it is dissipated in the manner already described above.

In another alternative arrangement, the invention may be made with a conventional flat or concave antenna reflector 52, with a corresponding sacrifice in the heat dissipation capability of the antenna array.

Any of the above-described arrangements of the invention may be made with still another variation in its construction. Each of the antenna dipole elements 40 is made in the form of a heat pipe having its interior walls and ends lined with a wicking material 58. Also, each dipole element 40 is completely enclosed and contains its own supply of 'heat transfer fluid 60. Fluid 60 cycles within the cavity of each dipole element 40 in a manner already described above for support post 50, taking 011 heat from enclosure 46 and removing it to the outside end of each dipole 40, where it is radiated to space.

'From the foregoing it may be seen that applicant has invented a novel type of microwave power receiving antenna capable of more eificient dissipation of heat than antennas previously known. The outputs from the individual dipole antennas may be connected either in series, in parallel or in series parallel, as desired. Also, diodes 42 may be mounted directly in the cavity of support post 50 to improve heat transfer efflciency, provided they are properly insulated electrically and the appropriate electrical connections are made through the upper end of support post 50. This approach, although more difficult from the standpoint of fabrication, is desirable at high power levels.

Of the various embodiments described in detail above, the embodiment which has support posts which communicate with the antenna reflector and which also has heat pipe conducting dipole elements is, of course, the most eflicient. The simpler embodiments, although they sacrifice efliciency which is highly desirable in the invention, do have the advantage of being cheaper and easier to manufacture.

What is claimed is:

1. A microwave power receiving antenna comprising:

(a) at least one pair of dipole antenna elements,

(b) at least one dipole center enclosure, the inside ends of each pair of said antenna elements being mounted on one said enclosure,

(0) a rectifying circuit in each said enclosure, said rectifying circuit comprising a plurality of diodes,

(d) at least one support post, each said enclosure being supported by one said support post,

(e) an antenna reflector, each said support post being mounted on said antenna reflector.

2. The microwave power receiving antenna of claim 1 wherein each said support post comprises:

(a) a cylindrical section of pipe having two closed ends,

(b) a fluid contained inside said pipe, for absorbing heat at the end of said pipe attached to said center enclosure, and discharging heat to said antenna reflector at the end of said pipe attached to said antenna reflector,

(c) a wick positioned along the inner surfaces of said cylindrical section of said pipe and said pipe ends, for returning said fluid from said end of said pipe attached to said antenna reflector to said end of said pipe attached to said diode enclosure.

3. The microwave power receiving antenna of claim 2 wherein said antenna reflector is a completely enclosed, flat, double-wall enclosure, said enclosure containing:

(a) a fluid for absorbing heat at the point of attach ment of each said support post to said antenna reflector and discharging the absorbed heat to points on the surface of said antenna reflector remote from poinst of attachment of each said support post, so as to distribute the absorbed heat to the whole surface area of said antenna reflector,

(b) a wick positioned on substantially all of the inner surface area of said antenna reflector, for returning said fluid from said remote points to said point of attachment of said support post.

4. The microwave power receiving antenna of claim 3 wherein each said dipole antenna element comprises:

(a) a cylindrical section of tubing having two closed ends,

(b) a fluid contained inside said tubing, for absorbing heat at the end of said tubing attached to said center enclosure and discharging heat at the opposite end of said closed section of tubing,

(c) a wick positioned along the inner surface of said tubing for returning said fluid from said opposite end of said tubing to said end of said tubing mounted on said center enclosure.

5. The microwave power receiving antenna of claim 1 wherein:

(a) each said support post comprises an enclosed,

cylindrical section of pipe,

(b) said antenna reflector comprises an enclosed, flat, double-wall enclosure, the enclosed area of each said support post communicating with the enclosed area of said antenna reflector, to form a total enclosed area including the enclosed areas of each said support post and said antenna reflector,

(c) said total enclosed area containing:

(1) a fluid for absorbing heat from said center enclosure and discharging the absorbed heat to points on the surface of said antenna reflector remote from points of attachment of each said support post, so as to distribute the absorbed heat to the whole surface area of said antenna reflector,

(2) a wick positioned on substantially all of the inner surface areas of said antenna reflector and each said support post, for returning said fluid from said remote points to said end of each said support post attached to said center enclosure.

6. The microwave power receiving antenna of claim 5 wherein each said dipole antenna element comprises:

(a) a cylindrical section of tubing having two closed ends,

(b) a fluid contained inside said tubing, for absorbing heat at the end of said tubing attached to said center enclosure and discharging heat at the opposite end of said closed section of tubing,

(c) a wick positioned along the inner surface of said tubing for returning said fluid from said opposite end of said tubing to said end of said tubing mounted on said center enclosure.

References Cited UNITED STATES PATENTS 3,432,690 3/1969 Blume.

ROBERT K. SCHAEFER, Primary Examiner H. I. HOHAUSER, Assistant Examiner US. Cl. X.R. 

